This invention relates generally to a motor controller. More specifically, to applications providing feedforward supply voltage for a sensorless or sensored motor controllers to maintain improved speed regulation.
Speed regulation in motor controllers is often achieved by determining or measuring the speed of the motor and utilizing the speed in one ore more controller loops. For example, in some systems speed may be measured using a speed measuring sensor such as a tachometer. Speed sensors, or detectors of various types are well known in the art. In recent years the application of speed detection to motor control functions has stimulated demands on the sophistication of these sensors. In other systems, motor speed may be computed by evaluating the time rated of change of a position of the motor. In some systems motor speed may be estimated employing computational methodologies based on motor parameters and the like without employing a speed sensor.
One technique to estimate speed is known as sensorless commutation whereby a DSP (digital signal processor) or ASIC (application specific integrated circuit) integrates motor back-EMF of a non driven phase in a classic two-phase-on brushless DC (BLDC) system to derive an error signal. Unfortunately, such a system can only update (re-compute) a speed value during the neutral transition of each commutation state, at best. In PWM (pulse width modulated) systems, this signal is averaged over many commutation intervals which makes speed updates even less frequent.
Speed regulation for a motor is achieved where speed is known or estimated with sufficient accuracy. FIG. 1 depicts an existing motor control system with motor speed feedback. With this configuration for a controller, a speed variation must be resolved and then fed back to the a controller for the appropriate control corrections. Such corrections take time and as a result a speed deviation is experienced. It will also be appreciated that in such a system, where a direct current (DC) bus supply is employed, in the presence the DC bus voltage disturbance will result in a deviation of the voltage supplied to the motor and thereby, a speed variation. In this situation, when a disturbance of the DC bus voltages results in a motor speed disturbance, the speed disturbance is not detected until the speed sensor (or speed estimation algorithm) can resolved and ascertain the changing speed. As a result the motor speed is disturbed as the DC bus voltage varies. Such a variation in motor speed is often undesirable and may be unacceptable is some systems. In other words, to compensate for speed variations, a the motor control system must wait for the sensor to make the next mechanical revolution to determine speed. If a DC bus disturbance has compromised speed, it will not be known until the sensor indicates so. It should be noted that some systems use multiple sensors, e.g., a sensor every n degrees, to acquire more frequent updates. Therefore, a system and methodology for controlling motor speed more directly responsive to DC bus voltage is needed.
Disclosed herein in an exemplary embodiment is a system for controlling a motor comprising: a voltage source including a voltage sensor for detecting a voltage of the voltage source; a motor in operable communication with an inverter, the motor responsive to a command signal from the inverter, the inverter is in operable communication with the voltage source and a controller. The inverter includes a plurality of switching devices configured to receive a command from a controller and generate a voltage command to the motor. The system also includes a controller in operable communication with the inverter and the voltage sensor; the controller configured to provide a command to the inverter responsive to the voltage of the voltage source.
Also disclosed herein in another exemplary embodiment is a method for controlling a motor comprising: receiving a voltage signal indicative of a voltage on a voltage source; receiving a speed command indicative of a desired speed for a motor; generating a voltage command to control a speed of the motor based on the voltage signal and the speed command; and the generating includes a feedforward voltage regulation function responsive to the voltage signal.